It has long been known to treat, e.g., demineralize, aqueous solutions, such as water, using ion exchangers and to regenerate these ion exchangers after demineralization or other treatment of the solution so as to replenish the ion exchangers for further treatment of the aqueous solution. Traditional ion exchangers are known cation and anion exchange resins, which are generally particulate materials in the form of granules, beads or grains, but can also be fibers, sheets and other forms. The ion exchangers are placed in filter containers through which the aqueous solution to be treated is consecutively piped so as to thoroughly contact the respective ion exchanger resins.
While the prior art regeneration of ion exchangers has been accomplished largely by supplying special acids and/or caustic solutions to the ion exchange materials, electrolytic processes have recently become known in which the ion exchangers are subjected to electrical voltage fields to produce an exchange of metal ions and the like by using the respective regeneration ions generated at the electrodes.
In such a previously known process according to DE-OS 38 05 813, regeneration of the ion exchangers is proposed by subjecting the ion exchangers to electrical voltage fields which exert a pulsating action on the ion exchangers and additionally have AC voltages superimposed on them to accelerate the regeneration of the ion exchangers.
Another process for treating aqueous solutions with regenerative treatment of the ion exchangers is shown in my earlier U.S. Pat. No. 4,636,296, in which electrode chambers are provided in a common vessel with various treatment chambers for loosening and regenerating the ion exchangers. The individual chambers, which are permeable to the migrating ions, are separated from each other by ion exchange membranes.
In these processes, some problems, mostly concerning the regeneration of the anion exchangers, may occur both in the functional aspects and in the equipment design. Thus, despite the high investment in chemical engineering and apparatus, it is not always possible to achieve sufficiently large regenerating capacities such as are known from traditional regeneration using supplied regenerating chemicals. Particularly, anionic salt components which require high concentrations of hydroxides for their desorption cannot always be removed during regeneration by electrical voltage fields. The reason for this poor performance is the high electrical resistance frequently exhibited by anion exchangers. This high resistance requires high electrical voltages to overcome the resistance which, in turn, results in an ionic current of a lower and hence insufficient concentration.
As a result, expensive equipment designs have been required in prior electrolytic regeneration systems. And, even with these expensive systems, the described problems still may produce an unsatisfactory regenerating action. This naturally results in a poor demineralization system and poor demineralization quality.